Blower Motor Malfunction
Blower Motor Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The HVAC control module applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:
* Low speed - 4 resistors
* Medium 1 speed - 3 resistors
* Medium 2 speed - 2 resistors
When the operator requests High speed, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.
Diagnostic Aids
Be sure the blower motor housing is not shorted to a grounded surface causing the blower motor to run continuously at high speed.
Reference Information
Schematic Reference
HVAC Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
* Air Temperature Description and Operation (Air Temperature Description and Operation)
* Air Delivery Description and Operation (Air Delivery Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for Scan Tool Information
Circuit/System Verification
1. Ignition ON, command the blower motor ON and OFF by switching the blower motor switch from the 0 position to the 4 position, the blower motor should turn ON and OFF when changing between the commanded states.
• If the blower motor does not turn ON and OFF, refer to Blower Motor Inoperative
2. Listen to the function of the blower motor while commanding the blower motor speed from Off through to the High speed positions using the blower motor switch, the blower motor speed should turn ON and the speed should vary from Low through High.
• If the blower motor speed does not change, refer to Blower Motor Malfunction.
Circuit/System Testing
Blower Motor Inoperative
1. Ignition OFF, disconnect the HVAC BLOWER HIGH relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. With the blower motor switch set to the 4 position, verify that a test lamp illuminates between the relay coil control circuit and ground.
• If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal and the HVAC BLOWER fuse is open, test or replace the HVAC BLOWER HIGH relay.
4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit for a short to ground.
5. Disconnect the harness connector at the blower motor.
6. Test for less than 1.0 ohm of resistance between the blower motor ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the blower motor.
8. Connect a 30A fused jumper wire between the relay switch B+ circuit terminal and the relay controlled output circuit terminal. Verify the blower motor is activated.
• If the blower motor does not activate, test the output circuit for an open/high resistance. If the circuit tests normal, test or replace the blower motor.
9. Connect a test lamp between the relay coil control circuit terminal and the relay coil ground circuit terminal.
10. Command the HVAC BLOWER HIGH relay ON and OFF by switching the blower motor switch from the 0 position to the 4 position. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
11. If all circuits test normal, test or replace the HVAC BLOWER HIGH relay.
Blower Motor Malfunction
1. Ignition OFF, disconnect the harness connector at the blower motor resistor assembly.
2. While changing the fan speed switch between the Low, M1 and M2 positions, verify that a test lamp illuminates between ground and the appropriate blower motor control circuit terminals listed below:
* Low terminal D
* M1 terminal A
* M2 terminal B
• If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the HVAC control module.
3. Ignition OFF, connect the harness connector at the blower motor resistor assembly and disconnect the blower motor.
4. Ignition ON, connect a test lamp between the blower motor control circuit terminal B and the blower motor ground circuit terminal A.
5. Cycle the fan speed switch between the Low, M1 and M2 positions. The test lamp should illuminate and change in intensity as the blower speed is varied.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor resistor assembly.
• If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, replace the blower motor resistor assembly.
6. If all circuits test normal, test or replace the blower motor.
Component Testing
Blower Motor Test
1. Ignition OFF, disconnect the harness connector at the blower motor.
2. Install a 30-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the control circuit terminal A and ground. Verify the blower motor activates.
• If the blower motor does not activate, replace the blower motor.
Relay Test
1. Ignition OFF, disconnect the HVAC BLOWER HIGH relay.
2. Test for 60-200 ohms of resistance between terminals 85 and 86.
• If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less than infinite resistance, replace the relay.
4. Test for less than 2 ohms of resistance between terminals 30 and 87A.
• If greater than 2 ohms, replace the relay.
5. Install a 3-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Measure for less than 2 ohms of resistance between terminals 30 and 87.
• If greater than 2 ohms, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning) for HVAC control module setup, replacement, and programming